The present invention pertains to an operator for a railroad track switch and, more particularly, to an improved cylinder head assembly for a pneumatically driven operator.
Railroad track switch operators or switch machines of the prior art are powered by a number of different types of actuators. Pneumatic cylinders and hydraulic cylinders are commonly used with the piston rods of such cylinders operatively connected to the switch points to selectively move the points between the two positions. Electric motor and fluid motor-driven actuators are also used. In addition, many switch operators also provide the capability for alternate manual operation.
In a railroad yard, a large number of switch points may be used and they are typically connected to a central monitoring and control system for automatic or semi-automatic operation. The operation of multiple switch points also typically includes a common electric power supply for operating valves and a common pressurized fluid supply for pneumatic or hydraulic cylinder operators. Thus, pneumatic switch operators are connected to a common source of compressed air and the operating valves used to control the pneumatic cylinders receive electric power from a common electric power supply line. In the United States, the railroad industry has adopted both 12 volt and 24 volt DC as standard switch operator power supplies.
The use of two different operating voltage standards has resulted in difficulties in operator repair and replacement and has also resulted in operational difficulties within a given system. Twelve volt operators may operate adequately over a voltage range between about 9 and 14 volts, whereas 24 volt operators may operate adequately over a range of about 19 volts to 26 volts. However, neither type of operator will operate in the voltage range needed to power the other type of operator and, furthermore, there is a dead band of about 4 to 6 volts between the respective ranges where neither operator will work. In addition, typical line voltage drops in large 24 volt systems often result in voltage variations that adversely affect operation or drop so low as to prevent operation.
Prior art pneumatic operators, though made to effect a point switch in about 0.5 second, would benefit from faster operation, particularly where the operator is subject to voltage variations due to line voltage losses and the like. Tracks switch operators of the prior art have also been characteristically difficult to service and repair. Electric power for the operating valve and compressed air to supply the motive force for the cylinder are typically supplied directly to the cylinder head. Removal and replacement of the valve typically requires manual disconnection of a number of electric leads and the removal of mounting bolts for the valve, all in a time consuming and inefficient manner. These maintenance and service problems are compounded when they must be performed in cold or other inclement weather.
In accordance with the present invention, an improved cylinder head assembly is provided for a pneumatic railroad track switch operator that addresses and eliminates or substantially improves all of the problems in prior art operators. The typical prior art pneumatic track switch operator includes a solenoid-operated spool valve that directs compressed air from a source to the piston of a double acting pneumatic cylinder. A prior art cylinder head may include a mounting surface for the spool valve and is further provided with internal air flow porting to control the flow of compressed air and exhaust air to and from the cylinder. Such porting typically includes a compressed air inlet port, a first supply passage that directs compressed air to one side of the piston to stroke the piston in a first direction and receives exhaust air from the same side of the piston when the piston is stroked in the opposite direction, a second supply passage that directs compressed air to the other side of the piston to stroke the piston in the opposite direction and receives exhaust air from that other side of the piston when the piston is stroked in the first direction, a first exhaust port that receives air from the first supply passage and a second exhaust port that receives air from the second supply passage. In accordance with the present invention, the improved cylinder head assembly comprises means for interconnecting the first and second exhaust ports to permit the flow of exhaust air from either of said supply ports to pass through both of the exhaust ports; recessed portions in the cylinder head for receiving electric power connections for operating the spool valve; voltage control means for applying 12 volt electric operating power to the spool valve from line voltage in excess of about 14 volts and for passing line voltage between about 14 volts and a minimum operating voltage directly to the spool valve; the voltage control means comprising a control module that is received in one of the recessed portions in the cylinder head; and interface means in another of the recessed portions of the cylinder head that defines the valve mounting surface for receiving the spool valve and provides direct connection to the ports and plug-in electric power connection to the voltage control module.
The voltage control module is preferably operative over a voltage range of from about 26 volts to about 9 volts. The module includes means for converting line voltage in the range of about 26 volts to about 14 volts to an operating voltage of about 12 volts. The module also includes means for passing line voltage in the range of about 14 volts to about 9 volts directly to the valve.
In the improved cylinder head assembly of the present invention, the interface means includes a first internal passage extending between said recesses and an operating power electrical conductor in the passage connecting the voltage control module and the plug-in connection. The cylinder head also includes a second internal passage and a line voltage power conductor within the second passage providing electric power at line voltage to the control module.